They worked fine for the tests but I quickly realized I needed something bigger. I went ahead and ordered some of these (Kelling, KL23H2100-30-4BM):
They are $59 a piece with 495 oz-in torque. I will be using one for each of me x and y axes and the smaller stepper for my Z axis. What these bigger steppers provide me is more speed and power. I am able to run the mill twice as fast with these steppers without skipping a single step.
I also got some new pure carbide bits in the mail for milling PCBs from Think & Tinker. I have yet to try them out, though I have complete confidence that they are up for the task.
I also ordered some carbide drill bits.
I'm looking forward to giving these a go soon.